Drug resistance to antibiotics, especially β-lactam antibiotics such as penicillin, cephalosporin and related compounds is one of the most serious problems in the treatment of infectious diseases (Neu, Science, 257, 1064–1073 (1992)). It represents not only a significant medical problem but a major public health and economic burden. Between 1980 and 1992, the death rate, due to infectious diseases as the underlying cause of death, increased 58%, from 41 to 65 deaths per 100,000 population in the U.S. Age adjusted mortality from infectious diseases increased 39% during the same period. Infectious disease mortality increased 25% among those aged 65 years and older (from 271 to 338 per 100,000) and 6.3 times among 25–44 year olds (from 6 to 38 per 100,000). Mortality due to respiratory tract infections increased 20% (from 25 to 30 deaths per 100,000). Reports from the Center for Disease Control (CDC) indicate that two million Americans acquire infections in hospitals each year, the cost of which runs to an estimated $4.5 billion. Of these infections, 70% are due to microbes that are resistant to one or more antibiotics and in 30–40% of the infections the causative microbe is resistant to first line treatment. The rate at which patients acquire infections in hospitals rose by 36% in 1995 compared with 1975. In 1995, 35.9 million patients entered hospitals in the U.S. compared with 37.7 million patients in 1975. For the same period, lengths of hosptial stays dropped to an average of 5.3 days from 7.9 days due to managed health care guidelines. However, the number of infections per 1,000 patient days rose to 9.77 from 7.18.
Without being limited to any particular theory or mechanism of action, it is believed that evolutionary selection and genetic transformation have made this problem pressing. Most antibiotic drugs are derivatives of naturally occurring bactericides (Davies, Science, 264, 375–382 (1994)), and many resistance mechanisms evolved long ago. Human use of antibiotics has refined these mechanisms and promoted their spread through gene transfer (Davies, Science, 264, 375–382 (1994)). A resistance mechanism originating in one species of bacteria can be expected to spread throughout the biosphere.
β-lactam antibiotics inhibit bacterial cell wall biosynthesis (Tomasz, Rev. Infect. Dis., 8, S270–S278 (1986)). They form covalent complexes with and consequently inactivate a group of transpeptidases/carboxypeptidases called the Penicillin Binding Proteins (PBPs). PBP inactivation disrupts cell wall biosynthesis, leading to self-lysis and death of the bacteria. β-lactam antibiotics have been widely prescribed. In the absence of resistance, β-lactams are the first choice for treatment in 45 of 78 common bacterial infections (Goodman & Gilman's The Pharmacological Basis of Therapeutics (Hardman et al., eds., McGraw-Hill, New York, 1996)).
Bacterial adaptations to β-lactam drugs (e.g., amoxicillin, cephalothin, clavulanate, and aztreonam) are among the best studied and most pernicious forms of antibiotic resistance. Without being limited to any particular theory or mechanism of action, it is believed that bacteria use several different mechanisms to escape from β-lactam antibiotics (Sanders, Clinical Infectious Disease, 14, 1089–1099 (1992); Li et al., Antimicrob. Agents Chemother., 39, 1948–1953 (1995)). Probably the most widespread is the hydrolysis of β-lactams by β-lactamase enzymes.
β-lactamases are endogenous bacterial enzymes that destroy β-lactam antibiotics and eliminate their efficacy. The name derives from their ability to cleave the β-lactam ring. The structures of many β-lactamases are known at the atomic level and available in the protein database. At least four classes of β-lactamases are known: Classes A, B, C and D. At the clinical level, the most important β-lactamases belong to Class A (TEM) and Class C (AmpC). TEM and Amp-C are serine hydrolases and have a critical serine in their catalytic site. TEM and AmpC) among different bacterial species share high sequence identity and structural similarity (Galleni, et al., Biochem. J., 250, 753–760 (1988); Galleni, et al., Biochem. J., 250, 753–760 (1988); Usher et al., Biochemistry, 30, 16082–16092 (1998)).
One way to overcome the negative effects of β-lactamases is to use molecules that neutralize the action of β-lactamase (known as β-lactamase inhibitors or inhibitors of β-lactamase) in combination with antibiotics. The three β-lactamase inhibitors currently in clinical use (clavulanic acid, sulbactam and tazobactam) are all transition state analogs that utilize the same β-lactam core that is present in the antibiotics themselves.
The similarity between the β-lactam antibiotics and β-lactam-based β-lactam-based β-inhibitors has proven to be a serious problem. Resistance to such β-lactam-based β-lactamase inhibitors arises through modifications of previously susceptible mechanisms. Certain mutations in β-lactamase, for example, reduce the effectiveness of β-lactam-based β-lactamase inhibitors while preserving the ability of the β-lactamase to hydrolyze the antibiotic molecules. Certain point substitutions in β-lactamases allow the enzymes to hydrolyze compounds designed to evade them (Philippon et al., Antimicrob. Agents Chemother., 33, 1131–1136 (1989)). Other substitutions reduce the affinity of β-lactam inhibitors for the enzymes (Saves, et al., J. Biol. Chem., 270, 18240–18245 (1995)) or allow the enzymes to simply hydrolyze them. Furthermore, several gram-positive bacteria (e.g., Staph. Aureus) have acquired sensor proteins that detect β-lactams in the environment of the cell (Bennet and Chopra, Antimicrob. Agents Chemotherapy, 37, 153–158 (1993)). β-lactam binding to these sensors leads to transcriptional up-regulation of the β-lactamase. β-lactam-based β-lactamase inhibitors, thus, can induce the production of the enzyme that they are meant to inhibit, preventing or reducing their efficacy.
Without being limited to any particular theory or mechanism of action, it is believed that one reason that bacteria have been able to respond rapidly with “new” resistance mechanisms to β-lactam-based inhibitors is that the mechanisms of action of the inhibitors are not, in fact, new, because β-lactamases have evolved mechanisms for, e.g., sensing and/or hydrolyzing such molecules. Accordingly, as long as medicinal chemistry focuses on β-lactam-based molecules to overcome β-lactamases, resistance can be expected to follow shortly.
One way to avoid recapitulating this “arms race” between bacteria and β-lactams is to develop non-β-lactam inhibitors that have novel chemistries and are dissimilar to β-lactams. Such non-β-lactam inhibitors would not themselves be degraded by β-lactamases, and mutations in the enzymes would not be expected render such inhibitors labile to hydrolysis. Such novel inhibitors would also escape detection by β-lactam sensor proteins that up-regulate β-lactamase transcription, and may be unaffected by porin mutations that limit the access of β-lactams to PBPs. Such inhibitors would allow the current β-lactam antibiotics to effectively work against bacteria where β-lactamases provide the dominant resistance mechanism.
It has previously been reported that boric acid and certain phenyl boronic acids are inhibitors of certain β-lactamases (Koehler and Lienhard, (1971); Kiener and Waley, Biochem. J., 169, 197–204 (1978) (boric acid, phenylboronic acid and m-aminophenylboronate); Beesley et al., Biochem. J., 209, 229–233 (1983) (twelve substituted phenylborinic acids, including 2-formylphenylboronate, 4-formylphenylboronate, and 4-methylphenylboronate; and Amicosante et al., J. Chemotherapy, 1, 394–398 (1989) (boric acid, phenylboronic acid, m-aminophenylboronate and tetraphenylboronic acid)). m-(dansylamidophenyl)-boronic acid has been reported to inhibitor of the Enterobacter cloacae P99 β-lactamase (Dryjanski and Pratt, Biochemistry, 34, 3561–3568 (1995)). In addition, Strynadka and colleagues used the crystallographic structure of a mutant TEM-1 enzyme-penicillin G complex to design a novel alkylboronic acid inhibitor [(1R)-1-acetamido-2-(3-carboxyphenyl)ethane boronic acid] with high affinity for this enzyme. (Strynadka et al., Nat. Struc. Biol., 3, 688–695 (1996)).
Additional boronic acid-based compounds with demonstrated or potential ability to inhibit b-lactamases have been reported in Tondi et al. (Chemistry & Biology, 8, 593–610 (2001), Martin et al. (Bioorganic & Medicinal Chemistry Letters, 4(10), 1229–1234 (1994), Weston et al. (J. Med. Chem., 41, 4577–4586 (1998) and U.S. Pat. Nos. 6,075,014 and 6,184,363.
Many of the compounds described above are peptide derivatives or peptidyl mimetics which are not desirable as orally available pharmaceutical drugs due to their rapid degradation by digestive enzymes (Ness et al, 2000; Morandi et al, 2003, Rudgers et al, 2001).
Hence, there remains a need for new non-β-lactam-based β-lactamase inhibitors that are active against a wide variety of β-lactamases, particularly those that are resistant to clavulanic acid, sulbactam and tazobactam.
Citation or identification of any references in the “Background of the Invention” or anywhere in the specification of this application is not an admission that such references available as prior art to the present invention.